Buying a Used Xbox, Suggestions?

Hello all,
I am looking to purchase a used Xbox in the next few days and was wondering what I should be looking for. Are there certain revisions that are more reliable, any known problems I should be aware of, etc?
Thanks!

Let's see check the manufacturing date, try to avoid anything earlier then 2003
DVD rom drive comparison
http://www.llamma.com/xbox/Repairs/xbox_dvd_version_comparison.htm
You want a samsung or a phillips, thompson drives struggle to read discs even when they are perfect

Problems? Sometimes video failure, sometimes dvd drive failure, most of the stuff is pretty easy to to fix. Nothing like a good xbmc.....

If you can a get a used one of any of the new models like mid to late 09 you'll pro be best, the new arcades are pretty decent as far as fan sound goes, and the overheating isn't so bad with these models.
But, you will have to by the harddrive. If your going to go for a used pro I'd say 08's aren't that bad, thats what I have and mine isn't that horrible. I've had some issues other than the RROD or e-74. but, nothing I haven't been able to repair myself.